This application relates to a process of treatment of raw molluscan shellfish, and more particularly to a process for destroying bacteria in shellfish, such as for example oysters.
In recent years, considerable attention has been paid in the media to tragic results of consumption of raw oysters where the individuals became infected with life threatening pathogenic organisms. Such bacteria as Vibrio Vulnificus live in marine environment, especially in warm waters, usually higher than 25xc2x0 C.
Vibrio Vulnificus has been isolated from estuarine and marine waters of the U.S. Gulf Coast, east coast, and west coast; it was also reported on other continents. The bacteria may transfer from water to the shellfish inhabiting the body of water, especially filter-feeding mollusks, where bacteria can multiply mostly in the gut region.
Vibrio is a genus of motile curved and rod-shaped Gram-negative bacteria. Other well-known vibriones are Vibrio cholerae and Vibrio Parahaemolyticus. Vibrio Parahaemolyticus is a common cause of gastroenteritis in some cultures, where consumption of food is particularly high, such as for example Japan.
Vibrio Vulnificus is a halophilic species, the strains of which are similar to Vibrio Parahaemolyticus and Vibrio alginolyticus. Vibrio Vulnificus thrives in warm waters. Ingesting uncooked or undercooked shellfish that contain vibrios, especially oysters, transmits it. After a brief incubation period, often as short as two hours, Vibrio Vulnificus causes septicemia and cellulitis. Physical symptoms include indigestion, cramps, nausea, vomiting, headache, weakness, fever and chills.
Usually, this food poisoning subsides spontaneously within two days. Occasionally, however, it is more severe. Persons with pre-existing hepatic disease or compromised immune system are especially in danger. Infection may occur not only through digestion of raw seafood but also from wound infection following exposure to seawater.
While fatal outcomes are extremely rare, the unfortunate events have been widely publicized, making the public aware of a potential life threatening exposure to the Vibriones. The fear of the bacteria poisoning is so high that the federal government issued a special warning advising the public of the potential dangers of raw oyster consumption. It has also been suggested that no harvesting of oysters be conducted during warm months in the Gulf of Mexico, so as to minimize the health risk associated with such food poisoning.
Public fear of the potential dangers associated with bacteria poisoning through raw oyster consumption adversely affected an important Louisiana industryxe2x80x94oyster harvesting. Market share of Gulf oysters shrunk, and many fishermen found that even oysters harvested from safe beds are not in such a great demand as they used to be and that the price has fallen drastically.
Still, consumption of raw molluscan shellfish is so widespread in the South that many restaurants continue to carry raw oysters as part of their menu. Even though many restaurants post a warning sign of the possible danger to a segment of the public with liver or immune system disorders it rarely stops dedicated gourmands.
To prevent poisonous consumption of pathogenic organisms, various methods have been suggested for treating raw shellfish, for example with heat or irradiation, in an effort to eliminate or minimize the public health danger. For example, Pat. No. 5,679,392 (the ""392 patent) issued on Oct. 21, 1997 for xe2x80x9cHeat Treatment of Raw Molluscan Shellfishxe2x80x9d discloses a method for preparing raw molluscan shellfish in the shell or out of the shell employing a mild heat treatment and cold storage.
According to the ""392 patent, the shellfish placed in a polymer or metallized bag is lowered into a circulating bath of water at a temperature of between 120xc2x0 F.-130xc2x0 F. for 30-45 minutes, after which time it is cooled in a cold water bath to a temperature between 28xc2x0 F.-32xc2x0 F. The product is then transferred to a cool water bath, where it is retained for 15-20 minutes and becomes ready for storage in a refrigerated state at 32xc2x0 F.-34xc2x0 F. The patent disclosure asserts that the mollusk remains in a raw state and in the shell throughout the process, while the number of pathogenic bacteria is reduced to an undetectable level.
While this process may be satisfactory for some products, it is believed that heating of the shellfish will affect the sensory qualities of the product, making it less desirable for consumption as raw shellfish. Heat treatment as a means of controlling microorganisms and bacteria in food products results in diminished taste and reduced nutritional content. Therefore, elevated temperatures are considered unsatisfactory for processing of raw oysters where the purpose of the process is to retain sensory qualifies of oysters and sell them on a half-shell.
Ionizing irradiation was tested as one of the methods of destroying harmful bacteria in live shellfish. However, this process is relatively expensive and has not yet obtained approval by the Federal Food and Drug Administration. Other known attempts to purify raw oysters involve depuration, wherein oysters are soaked in a tank of water for days at a time in an attempt to purge and cleanse the mollusk of the bacteria. So far, there have been no reports on the success of this method in destruction of bacteria in raw oysters.
Other suggested methods of destroying Vibrio Vulnificus involve cold, freezing, vacuum packaging, use of GRAS (diacetyl) compounds, suspension relaying into offshore water, and food condiment treatment. While some of these methods are relatively simple to implement, most of them have problemsxe2x80x94either too expensive, ineffective, time consuming, or failed to receive FDA approval.
It was also suggested to refrigerate oysters immediately after harvesting at 7.2xc2x0 C. or less in an attempt to control multiplication of bacteria. However, cold treatment greatly reduces but does not eliminate bacteria present in oysters during harvesting for a storage period considered normal for shucked or shell stock oysters.
Heat treatment, for example at 50xc2x0 C. for 10 minutes, kills the bacteria; this method is currently used on a commercial scale for live shell stock oysters. However, this method also kills the oysters. Additional drawback of this method is that it is difficult to control the temperature of commercial size batches when the size and shell thickness of oysters differ from batch to batch.
Vacuum packaging combined with freezing tends to reduce the level of Vibrio Vulnificus. However, this method is relatively expensive, reduces quality, so that the product treated in this manner may not find a wide acceptance with the public. When diacetyl, an FDA approved preservative was used on raw oysters, at levels of 0.05% or greater, it demonstrated decrease in the level of the bacteria, but did not guarantee complete elimination thereof.
When oysters were relayed into high salinity environment of offshore waters, Vibrio Vulnificus bacteria were reported to decrease to a level found in oysters normally harvested in more cold months, where no reported cases of food poisoning were recorded. However, oyster predators and parasites are a factor with this very expensive method. The use of UV light and micro-filtration treatment of seawater did not depurate the bacteria from oyster tissue.
Some studies examined the effect of Tabasco sauce on freshly shucked oysters. In about ten minutes, the level of Vibrio Vulnificus on the surface of tested oysters was significantly reduced, but the levels of the bacteria within the oyster meat remained almost unaffected.
In recent years, a new technology has emergedxe2x80x94high pressure processing of foods. The leading manufacturer of high-pressure food processors is ABB Pressure Systems AB of Vasteras, Sweden and its affiliate, ABB Autoclave Systems, Inc. of Columbus, Ohio. According to industry sources, this company makes equipment for processing of juices, fruits, vegetables, fruit-based beverages, jams, sauces, soups and meats. The company""s literature claims that most bacteria in food can be killed by pressures in the range of 400-800 MPa (58,000 p.s.i.-116,000 p.s.i.).
A Canadian company, GEC ALSTHOM, developed a cold pasteurizing system, which utilizes high hydrostatic pressure for processing thermal-sensitive packaged food products. According to that company""s literature, pressure modifies cell membrane permeability of microorganisms. As a result, bacteria are inactivated or die. It is recommended that the treated products are kept chilled at 4xc2x0 C. in order to reduce bacteriologic risk. The process is said to triple shelf life of the products.
Other companies in Europe and the United States continue research in the highpressure food processing area.
High pressure is said to be preferable to heat treatment because high pressure does not destroy many of the substances found in fresh foods, such as vitamins, chlorophyll and aroma substances. As a result, refrigerated shelf life of fruit and vegetable products, as well as high-acid products can be increased from several weeks to several months. Most importantly for the purposes of the present invention, high pressure treatment is believed to increase food safety by reducing bacteria in the processed products, while retaining the products"" nutritional value, color, flavor and texture.
The principle of cold isostatic (uniformly applied) pressure processing is relatively simplexe2x80x94food is placed in a container and is surrounded by a pressure medium, usually water. An external pressure intensifier to a pre-determined value pressurizes the vessel. Pressure is fed into the pressure vessel where food products have been deposited. Pressure in such a vessel is distributed evenly through all parts of the product, thereby preventing mechanical damage of delicate food products. The process may be conducted with no or minimal heat treatment.
Another problem that the present invention addresses is mechanical shucking of oysters. Seafood processing plants employ skillful workers for the preparation of oysters for packaging in jars and other containers for sale to the customers. Restaurants that serve raw oysters also employ special personnel for shucking oysters before serving the delicacy on a half shell.
The process of oyster shucking involves cutting of the connective tissue of oyster adductor muscle that is normally attached to the shell and keeps the shell halves tightly closed. More experienced workers perform this task relatively well, while novices can damage the product and cut through the body of the oyster, thereby reducing the quality and increasing the cost.
At present, the applicant is not aware of any commercial utilized method of mechanical shucking of oysters. It is estimated that about 80% of the cost of a shucked oyster are due to the labor-intensive hand-shucking process.
The present invention contemplates elimination of drawbacks associated with the prior art and reduction or elimination of harmful bacteria in raw shellfish, as well as shucking of oysters without any substantial affect on the sensory qualities of raw shellfish. Additionally, a new method of fabricating the yoke and chamber of high pressure equipment is disclosed.
It is, therefore, an object of the present invention to provide a process for reducing or elimination of pathogenic organisms from raw molluscan shellfish, such as oysters, clams, and mussels.
It is another object of the present invention to provide a method of reducing harmful bacteria in raw shellfish without substantially affecting its sensory qualities.
A further object of the present invention is to provide a method of shucking oysters and other shellfish such as clams and mussels that does not involve manual cutting of the oyster muscle.
Still another object of the present invention is to provide an apparatus for high pressure processing of shellfish, such as oysters, clams and mussels.
These and other objects of the present invention are achieved through a provision of a process that includes high-pressure treatment of raw shellfish, the process comprising the step of exposing the shellfish to relatively high hydrostatic pressure. The process is conducted at ambient temperatures, exposing the molluscan shellfish to the liquid pressure of between 20,000 p.s.i. to 80,000 p.s.i. for 1-15 minutes.
As a result of the high-pressure treatment, pathogenic organisms, such as bacteria Vibrio Vulnificus are destroyed without substantially adversely affecting the sensory qualities of the shellfish. At the same time, the connective tissues of oyster adductor muscle holding the two oyster shell halves is separated from the shells, and the oyster shells open without any manual cutting of the muscle.